As Downton returns for a fourth series, here's our essential primer to a
television phenomenon. By Ceri Radford.

Set in 1922, the new series picks up six months on from Matthew Crawley's untimely death, an event which, when it aired in the Christmas special, felt like the TV equivalent of receiving a nice, shiny gift and then opening it to find a rotten fish. Given that in an earlier plot arc, Matthew (Dan Stevens) had gone from being crippled and impotent to leaping from his wheelchair to father an heir, it wouldn't have surprised me to see him miraculously reanimated with a sticking plaster on hisleft eyebrow.

Alas, no. He is resolutely deceased; a pall is cast over the house; his baby George - born the day of his death - is fatherless, and his widow Mary (Michelle Dockery) looks sepulchral, while her family frets. Some much needed sparkle will be provided by the carefree cousin Rose (Lily James), a permanent Downton fixture this series, while Lady Edith (Laura Carmichael) is still pursuing her writing career - and a married man - in London.

Below stairs, Bates (Brendan Coyle) and Anna (Joanne Froggatt) have picked up the Mary and Matthew baton of smug,happily married couple. For now.

Not strictly speaking a new character, but a fresh face and a surprise nonetheless: Edna Braithwaite (MyAnna Buring) is back. Remember her? No? Cast your mind back. She appeared - briefly - in series three as the pretty servant who set her maid's cap at the newly widowed Branson (Allen Leech). Here she makes an improbable return as a lady's maid, an appointment bound to cause romantic mayhem. Added to the mix below stairs is visiting valet Green (Nigel Harman), a malevolent charmer.

Meanwhile, Downton's first black character appears: handsome jazz musician Jack Ross (Gary Carr), who is rumoured to have his eye on Lady Mary, but could also put a spring in the step of the music-loving, rebellious Rose. And let us not forget the newest of new characters: baby George, who is in fact played by one of two twins (a handy trick, should the child become fractious: if only all actors were thus interchangeable).

Mary's suitors are circling

Lady Mary is inconsolable as the series opens; but for her son's sake - and ours - life must go on. Enter the new batch of toothsome suitors. First on the scene is Lord Gillingham (Tom Cullen), a childhood friend with dark good lucks which recall the unfortunate Mr Pamuk. Let's hope this one escapes the Lady Mary death curse. Alternatively, Charles Blake (Julian Ovenden) is a man more in Matthew's modernising mould: a Government researcher carrying out a study of crumbling country estates (gulp).

The scene is set for another enjoyable clash between family tradition and reform, accessorized with arch glares and evening gloves. Or will Lady Mary eschew all that, and Charleston off with the jazzy Jack Ross?

The celebrities are dropping in

In a coup which shows the global appeal of the show, the producers persuaded a bona fide opera star - New Zealand's Dame Kiri Te Kanawa- to play the illustrious Australian soprano Dame Nellie Melba, invited to sing at a grandiose Downton house party. Her performance on set was apparently so powerful it made cast and crew alike shed a tear: I just hope the on-site catering van didn't make the dame weep.

In another nod to the famous names of the era, Virginia Woolf will make a brief appearance, played byChristina Carty. She will probably rub shoulders with Edith at a literary soiree, though I would love to see a plot twist to in which Woolf confronts the Earl of Grantham over his "there there, little lady" attitude to women.

Downton has hit the roaring Twenties

The Twenties had started to whisper in the last series, but this time round they are set to roar. "I've learned so many different dances this series," says Lily James, who plays jazz-club-bothering Rose. In other words: do not despair; the drab mood of the opening episode will not last. Lady Edith steps out of her sisters' shadows and into an array of slinky, beaded evening dresses, the stiff corsets and even stiffer social restraints of earlier series a fading memory. Mrs Patmore (Lesley Nicol), meanwhile, grapples with the problems of modernity in the form of an egg whisk.

Downton Abbey cast members old and new

America hearts Downton

Americans like to view the British as uptight, emotionally repressed snobs with dark secrets and bad teeth. Downton Abbey confirms all of these suspicions - with the possible exception of our dentistry - and who doesn't enjoy being proven right? Downton fever is endemic in America: symptoms include nostalgia and slightly blurred critical faculties. More than 12 million people watched the last series, the show was nominated for 10 Emmy awards - the awards ceremony takes place tonight and you've got to bet on a few Downton gongs - and Michelle Obama requested advance copies of the latest episodes. Happily, this trend confirms our own prejudices that Americans are suckers for pseudo-historical schmaltz.

They're doing their best about the bloopers

Having visited the set of Downton and met an historical advisor stipulating which character would be expected to leave the room first, and a costume designer who laboriously sources scraps of vintage cloth, I have to say I sympathise with the programme when the inevitable historical bloopers appear. Glimpses of double-yellow lines, a television aerial and a modern conservatory have all caused apoplexy in the past, and most recently it was suggested their table settings are all wrong. But doubtless this well-funded new series will redouble its efforts to deliver a view of 1920s Britain unsullied by pesky anachronisms.

It's not going to be sad anymore

“We don’t want to have any more deaths at the moment, that’s for sure. At least not straight away." (William Hill has Bates 3-1 favourite to die next). Comfort, of a sort, from the executive producer, Liz Trubridge, and it's just as well: our affections for what is essentially feel-good TV would not withstand another blow of the Sybil-or-Matthew-violent-death magnitude. Instead, I predict births: Edith and Anna could add to the patter of little feet, upstairs and downstairs. Lord Grantham (Hugh Bonneville) will clash with Mary over plans to modernise the estate, while a softer side of the steel-clad Dowager Countess (Maggie Smith) will emerge.

Downton's bigger than Belgium

An estimated 120 million people in 220 countries have watched the series. Think of it: that's ten times the population of Belgium, all united under the flag of Downton, its sonorous opening theme tune their anthem. Where success leads, spoofs and spin-offs inevitably follow, from Mouseton Abbey (a children's book) to Downton Tabby (a cat-based YouTube parody). Even the American rapper P Diddy has got in on the act, declaring "I am an Abbey head, yes yes yes" and appearing superimposed in a montage of scenes from the show as "Lord Wilcock", succumbing to Thomas's (Rob James-Collier) advances and trying to sell the Earl of Grantham shares in IBM.

Gary Carr is Jack Ross

The new episode sparkles

The first episode marks a return to form, after a patchy third series and the sherry-spilling horror of the Christmas special. Always impressive, Michelle Dockery excels with a truly touching performance as a brittle widow struggling to see the point in fighting through her grief. Look out for a poignant scene where the Dowager Countess foregoes her usual barbs for some sincere, grandmotherly advice.

Below stairs, Mrs Hughes (Phyllis Logan) forces Mr Carson (Jim Carter) to confront a relic from his past that he'd rather forget. Though implausible in places, this is an enjoyable return for a series that, like the Countess herself, shows a tough hide and impressive longevity.